Problems with self combining bodies (of course undesired) solidworks BUG?

Hello,

I have hard problems with bodies that combine theme selves together out of the blue.

This is my history:

- the part was done in SLW 2013 and had no problems at all

-  I switched to SLW 2015 and added some modification to my file (this modification are located in the last part of the feature tree diagram, so can't change the older features)

- I noticed a problem: chamfer 7 -> error missing edge of the chamfer; the problem is due to the fusion of two bodies together.

If you try to go back on the past in the diagram tree, after "split 5" there was the division of that external shell in two parts.. but now this division doesn't exist anymore. This division dome back to live after "split 10" withot reason.

I want to remember that "Chamfer 7" didn't give me any error after the creation in SW 2013  (and even after the fist opening with SW 2015)

SolidworksParts And Features